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To study the behaviour of a carbon-fibre reinforced-plastic laminate under a biaxial stress state, a new type of cruciform specimen has been developed. This specimen is loaded biaxially under static and cyclic fatigue conditions. The experiments are monitored simultaneously using digital image correlation with two high-speed cameras and infrared thermography. A comparison between the measurements and a finite element model is used to validate the design of the sample.

International audience; This paper presents different interests of non destructive full-field measurement. More precisely, it focuses on the characterization and the comparison of the X-ray tomography and two methods of infrared thermography in order to define the defect detection limits and to precise the specific application fields for each technique on multi-layered and sandwich composite structures. The obtained results are qualitatively and quantitatively analyzed.

The use of multi-layered composite materials in the confection of industrial pipe connections (elbows, reduction pipes, flanges etc.) is often put off because of the high cost of manufacture. The aim of this study is to replace the multi-layer process (woven reinforcement-organic matrix) by sandwich process with a view to reducing the cost of manufacture. Validation is carried out on different structures: ring, cylinder with and without end effect, elbows and floating flanges.

This study presents the measurement of fields of displacement and deformations on butt joints in hydrostatic depression. The aim of this paper is to observe the general behaviour of the rubber. Various definitions of butt joints were tested in traction. We are interested on the types of fracture and the phenomenon of vacuolization, which occurs in the rubber.

In this paper, we report on the developed and used of finite element methods, have been developed and used for sheet forming simulations since the 1970s, and have immensely contributed to ensure the success of concurrent design in the manufacturing process of sheets metal. During the forming operation, the Gurson–Tvergaard–Needleman (GTN) model was often employed to evaluate the ductile damage and fracture phenomena. GTN represents one of the most widely used ductile damage model. In this investigation, many experimental tests and finite element model computation are performed to predict the damage evolution in notched tensile specimen of sheet metal using the GTN model. The parameters in the GTN model are calibrated using an Artificial Neural Networks system and the results of the tensile test. In the experimental part, we used an optical measurement instruments in two phases: firstly during the tensile test, a digital image correlation method is applied to determinate the full-field displacements in the specimen surface. Secondly a profile projector is employed to evaluate the localization of deformation (formation of shear band) just before the specimen’s fracture. In the validation parts of this investigation, the experimental results of hydroforming part and Erichsen test are compared with their numerical finite element model taking into account the GTN model. A good correlation was observed between the two approaches.

This work deals with the Liquid Resin Infusion (LRI) process developed within the research program “FUSelage COMPosite” of DAHER SOCATA. This manufacturing process enables the realization of complex composite structures or fuselage elements in a single phase (mono-material), which considerably reduce connections and relative difficulties. The concern here is the investigation of non destructive testing (NDT) methods that can be applied to LRI-structures in order to define their capacities for defect detection, and especially their associated critical defect size. In aviation industry, the AITM standards require the ultrasonic testing as NDT for composite materials. Therefore the aim of this work is to characterize and compare three different and complementary ultrasonic techniques on composite specimens. Such analysis allows to define the NDT application field of each method in term of defect detection.

SUMMARY For lightweight structural components, continuous fibre-reinforced thermoplastic composites have demonstrated success in aerospace and defence applications. Their mechanical behaviour is a result of the possible sliding and interactions between the fibres, but the complex deformation mechanisms of this sheet are a main problem in the practical thermoforming process. In this context, a large experimental work was developed to analyse the behaviour of a 5-harness satin weave carbon–polyphenylenesulfide (PPS) composite. Firstly, we started this work with a microscope observation of the sheet cross section and a thermo-gravimetric analysis of carbon/PPS to understand the thermal condition in the forming process, the reinforcement (fibre and yarn) geometry and dimensions and the textile reinforcement architectures. Secondly, in high temperature conditions (at 320°C), static uniaxial and biaxial tensile tests were carried out. During these mechanical tests, we used a digital image stereo-correlation technique to get full field displacement measurements and an infrared camera to measure the temperature in the surface of sample. The results of the experimental investigation were used with the commercial software abaqus to develop a numerical model of stamp thermoforming operation. The stamp thermoforming part was developed using a hemispherical punch and compared with an experimental result. In the deformed part obtained by thermoforming of the carbon/PPS sheet, we analysed the instability phenomena such as wrinkling. Copyright © 2011 John Wiley & Sons, Ltd.

The present study analyses an aircraft composite fuselage structure manufactured by the Liquid Resin Infusion (LRI) process and subjected to a compressive load. LRI is based on the moulding of high performance composite parts by infusing liquid resin on dry fibres instead of prepreg fabrics or Resin Transfer Moulding (RTM). Actual industrial projects face composite integrated structure issues as a number of structures (stiffeners, …) are more and more integrated onto the skins of aircraft fuselage. A representative panel of a composite fuselage to be tested in buckling is studied numerically. This paper studies which of the real behaviours of the integrated structures are to be observed during this test. Numerical models are studied at a global scale of the composite stiffened panel. Linear and non linear analyses are conducted. The Tsai–Wu criterion with a progressive failure analysis is implemented, to describe the global behaviour of the panel up to collapse. Also, three stiffener connection methods are compared at the intersection between two types of integrated structures. Load shortening curves permit to estimate the expected load and displacements.

The numerical simulation based on the Finite Element Method (FEM) is widely used in academic institutes and in the industry. It is a useful tool to predict many phenomena present in the classical manufacturing forming processes such as necking, fracture, springback, buckling and wrinkling. But, the results of such numerical model depend strongly on the parameters of the constitutive behavior model. In the first part of this work, we focus on the traditional identification of the constitutive law using oriented tensile tests (0°, 45°, and 90° with respect to the rolling direction). A Digital Image Correlation (DIC) method is used in order to measure the displacements on the surface of the specimen and to analyze the necking evolution and the instability along the shear band. Therefore, bulge tests involving a number of die shapes (circular and elliptic) were developed. In a second step, a mixed numerical–experimental method is used for the identification of the plastic behavior of the stainless steel metal sheet. The initial parameters of the inverse identification were extracted from a uniaxial tensile test. The optimization procedure uses a combination of a Monte-Carlo and a Levenberg-Marquardt algorithm. In the second part of this work, according to some results obtained by SEM (Scaning Electron Microscopy) of the crack zones on the tensile specimens, a Gurson Tvergaard Needleman (GTN) ductile model of damage has been selected for the numerical simulations. This model was introduced in order to give informations concerning crack initiations during hydroforming. At the end of the paper, experimental and numerical comparisons of sheet metal forming applications are presented and validate the proposed approach.

As a complement to classic characterization in the identification of elastomers, full-field measurement methods such as image stereo correlation can undeniably contribute to the validation of elastomeric connection behaviour. Indeed, these measurements enable three-dimensional displacement and strains fields over the totality of the studied surface to be finely reached. Characterization tests in shearing on an elastomer were followed by image stereocorrelation up to high strain levels. The experimental results could thus be confronted with theoretical results using an Alexander hyperelastic behaviour law, which enabled the relevance of this law to be validated locally.

The hydroforming process is characterized in these recent years by the remarkable development to compare with other processes manufacturing such as deep drawing and bending... Hydroforming is a reliable process that improves the resistance and rigidity of parts with the geometrical and dimensional tolerances allowing for lower costs tool and therefore an overall cost of manufacturing reduced. The success of hydroforming process requires the control simultaneously of various parameters such as used material properties, thickness, internal pressure,... In this paper, we introduce our model based in a neural approach (ANN) compared to the numerical simulation and experimental results. This method allows a better thickness distribution during Tee extrusion tube hydroforming process (THF) and the optimization of the final part geometry. A multilayer’s neural networks (MNN) program is used to control the tube wall thickness variation, so the loading paths (axial feeding and the internal pressure) are used like inputs for our networks, the thickness is the output.

International audience; In this paper, errors related to digital image correlation (DIC) technique applied to measurements of displacements are estimated. This work is based on the generation of synthetic images representative of real speckle patterns. With these images, various parameters are treated in order to determine their impact on the measurement error. These parameters are related to the type of deformation imposed on the speckle, the speckle itself (encoding of the image, image saturation) or the software (subset size).

Super-pressure balloons developed by the Centre National d'Etudes Spatiales (CNES) provide a cheap, non-polluting, and quickly operable platform for in-situ measurements at altitudes of up to about 25 km, and for remote sensing of the earth, the atmosphere, and space from regions inaccessible to other means of transport over similar observation periods. They are lifted by a helium-filled, approximately spherical, closed envelope made of a polyethylene terephthalate (PET)-based multi-layer polymeric film. It appears that during working flights, these balloons may sometimes explode prematurely. For this reason, the CNES is carrying out research programme and experiments in order to predict better stability of balloon flight and guarantee a life span corresponding to the technical requirements. In this article, experimental results are presented concerning the identification and characterization of film damage induced by simple and triple wrinkling. The present authors started from microscopic observations of damage involving wrinkles and from unidirectional tensile tests of the damaged film with simple and triple wrinkles. During tensile tests, in order to observe the zone affected by wrinkling, an optical technique was used (electronic speckle pattern interferometry) to measure local strain in the damaged area. The correlation between the strain level in the wrinkles observed during tensile testing and the evolution of damage parameters depending on strain gives the damage parameter in the case of simple and triple wrinkling.

This work presents a new multilayered laminated composite structure model to predict the mechanical behaviour of multilayered laminated composite structures. This new multilayered structure model describes the shear stress distribution model through the thickness respecting free boundary conditions on the top and bottom surfaces by an exponential function. This model has the same order of complexity as Touratier's model ‘Sine’, so a shear correction factor is not required like in the first-order shear deformation theory. This model is more precise than all other existing refined theories. This theory is based on the kinematic approach in which the shearing is represented by an exponential function. The virtual power principal is used to deduce the boundary value problem. To verify the precision of the present model, several significant problems on bending, vibration, and buckling of laminated and sandwich structures have been studied. The results by the present model are compared with the exact three-dimensional elasticity theory and with several other well-known theories. The proposed model is found to be more precise for analysing multilayered structures.

International audience; Optical full-field measurement methods such as Digital Image Correlation (DIC) are increasingly used in the field of experimental mechanics, but they still suffer from a lack of information about their metrological performances. To assess the performance of DIC techniques and give some practical rules for users, a collaborative work has been carried out by the Workgroup "Metrology" of the French CNRS research network 2519 "MCIMS (Mesures de Champs et Identification en Mécanique des Solides / Full-field measurement and identification in solid mechanics, http://www.ifma.fr/lami/gdr2519)". A methodology is proposed to assess the metrological performances of the image processing algorithms that constitute their main component, the knowledge of which being required for a global assessment of the whole measurement system. The study is based on displacement error assessment from synthetic speckle images. Series of synthetic reference and deformed images with random patterns have been generated, assuming a sinusoidal displacement field with various frequencies and amplitudes. Displacements are evaluated by several DIC packages based on various formulations and used in the French community. Evaluated displacements are compared with the exact imposed values and errors are statistically analyzed. Results show general trends rather independent of the implementations but strongly correlated with the assumptions of the underlying algorithms. Various error regimes are identified, for which the dependence of the uncertainty with the parameters of the algorithms, such as subset size, gray level interpolation or shape functions, is discussed.

One of the current problems connected with multi-layer composite structures concerns the analysis of the distribution of the stresses around peculiarities (free edge and loaded edge) and at the interfaces of each layer. This work presents a new shear stress function in the form of the exponential function, to predict the mechanical behaviour of multi-layered laminated composite structures. As a case study, the mechanical behaviour of a laminated composite beam (90^o/0^o/0^o/90^o) is examined. The results are compared with the model ''Sinus'' and 2D finite element method studied. Results show that this new model is more precise than older ones as compared to the results obtained by the finite element analysis [Abaqus]. To introduce continuity on the interfaces of each layer, the kinematics defined by Ossadzow is used with the new exponential model. The equilibrium equations and natural boundary conditions are derived by the principle of virtual power.

Spherical plain bearings are used on many components of Airbus aircrafts like engine-to-pylon and pylon-to-wing links. Their design is based on contact pressure distribution on spherical surfaces. Until now, empirical laws are applied to determine it, and the aim of this work is to develop a numerical modelling in order to validate the use of these laws. The assumptions on the numerical model and their significance have been verified and meas-ured by scattered light photoelasticity (SLP) on an epoxy replica of the bearing. The analysis of this type of bearing is difficult due to its three-dimensional behaviour and its spherical confined contact. The SLP technique allows getting information on stress fields inside an epoxy specimen with the analysis of photoelastic fringes. Comparing photoelastic fringes with simulated results, the finite-element model has been improved to be more representative of the real life bearing. In addition, some critical factors on the bearing behaviour have been obtained.

Long duration super-pressure balloon design and manufacturing is a great challenge for the Centre National d'Etudes Spatiales in scientific ballooning. They are made of 50 μm thick polymer films polyethylene terephtalate/polyamide/polyethylene terephtalate which are joined with 23 μm thick adhesive polyethylene terephtalate bands. To date, during flight missions, a major problem appears: some balloons explode prematurely. This is why this study deals with the mechanical behaviour of the stratospheric pressurized balloons and particularly with the assembly of the constitutive films material. First, a nanoindentation test campaign makes it possible to identify the elastic properties of the materials at two different temperatures. Then, a nominal assembly is simulated in two stages: two-dimensional and three-dimensional. Finally, the factorial design method combined with finite-element simulations was used to study the influence of the various conception parameters on the mechanical behaviour of the assembly.

During airbag production, many parts are obtained by plastic deformation such as the lid of the gas generator. Since the airbag gas generator is a significant vehicle safety part, several pressure tests have been developed in order to prove the reliability of this product. A ductile fracture problem initialized by a localization of the deformation is observed along the blending radius. In order to understand the mechanical processes involved in the forming operation, a numerical and experimental study was developed. A tensile test specimen extracted from the sheet of study, undergoes elastic deformation that is followed by a transition to plastic deformation. Although during this stage of the test the deformation is stable, the strains begin to localize within a relatively broad zone known as diffuse necking. The stable deformation, with continuously rising load, is followed by the instability whereby a local neck or shear band is produced due to strong localization of deformation. The localization is explainable by the inhomogeneity in macroscopic material properties in the specimen. The necking behavior is a vital precursor to the final failure. A Digital Image Correlation (DIC) method is used in 2D and 3D to evaluate the necking and localization of deformation, which shows clearly the two stage of necking phenomena. Moreover, a numerical modeling was developed of tensile test under ABAQUS commercial software. In this model we use Gurson Tvergaard Needleman (GTN) ductile model of damage to predict the necking phenomenon. Furthermore the results from FE simulations are compared with experimental results from uniaxial tensile tests. Finally we develop the numerical model of the lid of the gas generator obtained by forming process.

In order to predict the flight parameters and to improve the life time of long duration super-pressure balloon, a research program on modelization and experimental simulation of the balloon envelope mechanical behavior is carried out. The balloon is a 10 m diameter type made with multilayer polymeric films and tapes. A facility was developed to measure, via a stereo-correlation system, the 3D displacement and the in plane solicitation strain of a 1.5 m diameter balloon envelope part in realistic flight conditions, i.e. pressure, temperature and loading at the sample boundaries. A time dependant non-linear Maxwell model of the polymeric material behavior was identified from uniaxial creep and relaxation tests and implemented in a Finite Elements code, simulating the sample tested in the facility. The Poisson ratio of the transparent and supple balloon film has been measured with an image correlation system. Experimental results are obtained both at room and in cold conditions (−60 °C) for various values of differential pressure. Vertical displacement and in plane 2D strain of apex part deduced from the numerical modeling are compared to experimental results.

Ce travail concerne la simulation numerique et experimentale du comportement mecanique des ballons pressurises stratospheriques. Ce programme de recherche entrepris par le CNES et l'ONERA est base sur (i) la modelisation du materiau polymere constitutif des ballons par des lois de comportement de type viscoelastique ; (ii) la simulation experimentale de sous-ensembles de ballons lors de phases de vol; (iii) la validation des lois viscoelastiques par comparaison essais/calculs du comportement de sous-ensembles de ballons. Le dispositif experimental utilise, nomme NIRVANA, reproduit les conditions de vol d'un ballon, i.e. la temperature, la pression et la contrainte dans l'enveloppe. Dans le cadre des caracterisations en grandes deformations des polymeres, l'instrumentation generalement mise en œuvre permet seulement d'acceder a des caracteristiques globales et macroscopiques. Le suivi de tels essais par la methode de stereo-correlation d'images, methode basee sur les principes de la photogrammetrie, permet d'acceder de maniere fine aux champs de deplacements et de deformations sur la totalite de la surface mesuree. Cette richesse d'information experimentale s'avere particulierement utile pour la validation non seulement globale mais aussi locale des lois de comportement utilisees.

Knowledge of edge effects in composite with honeycomb cores is essential for the design of sandwich structures. This paper deals with the measurement of strain by the application of reflection photoelasticity. Because of the geometry of honeycomb cores a classical method by strain gages is inaccurate and unsuitable. The measurements by photoelasticity is compared to an analytical and numerical results. The final aim of this work is to determine the behavior of such structures by the exact knowledge of its mechanical properties deduced in part from edge effect results.

Long duration super-pressure balloons constitute a great challenge in scientific ballooning. For any type of balloons (spherical, pumpkin, …), it is necessary to have a good knowledge of the mechanical behavior of envelopes regarding the level and the lifetime of the flight. For this reason CNES, ONERA and ENIT are carrying out a research program of modelization and experimentation in order to predict the envelope shape of a balloon in different conditions of temperature and differential pressure. This study was conducted in two parts. During the first one, we defined, with parameters obtained from unidirectional tests, the mechanical laws (elasticity, plasticity and viscosity properties of polymers) of materials involved in the envelope. These laws are introduced in a finite element code, which predicts the stress and strain status of a complex envelope structure. During the second one, we developed an experimental set-up to measure the 3D strain on a balloon subsystem, which includes envelope, assemblies and apex parts, in real flight conditions. This facility, called NIRVANA, is a 1 m3 vacuum chamber with cooled screens equipped with a stereoscopic CCD measurement system. A 1.5 m diameter sample can be tested under differential pressure, regulated temperature (from +20 to −120 °C) and a load (up to 6 tonnes) applied on tendons. This paper presents the first results obtained from the modelizations and measurements done on an envelope sample submitted to axisymmetrical stress due to the differential pressure. This sample consists of a 50 μm multilayer polymer film with an assembly, used in 10 m diameter STRATEOLE super-pressure balloons. The modelization gives results in good accordance with the experiments and will enable us to follow this work with cold conditions, time dependence (creeping) and more complex structures.

Resume Afin d'identifier le comportement mecanique de films plastiques transparents utilises pour la fabrication des ballons pressurises developpes par le CNES, une etude experimentale est realisee a partir de mesures sans contact par stereo-correlation d'images. Les deux cameras CCD permettent d'acquerir des images numeriques avec une definition de 1280 par 1024 pixels. Ces images sont ensuite traitees avec le logiciel ARAMIS (GOM France). Grâce a ce dispositif il est possible de mesurer apres calibrage les deplacements et les deformations a la surface d'un objet avec une resolution de 2000 μm/m en deformations et de 15 μm en deplacements. La faisabilite de la mesure sans contact par stereo-correlation a ete demontree tant sur des materiaux presentant la particularite d'etre transparents que dans les conditions imposees par la plate forme experimentale Nirvana, developpee a l'ONERA.

This work presents a new multi-layer laminated composite structure model to predict the mechanical behaviour of multi-layered laminated composite structures. As a case study, the mechanical behaviour of laminated composite beam (90°/0°/0°/90°) is examined from both a static and dynamic point of view. The results are compared with the model “Sinus” and finite element method studied by Abou Harb. Results show that this new model is more precise than older ones as compared to the results by the finite element method (Abaqus). To introduce continuity on the interfaces of each layer, the kinematics defined by Ossadzow was used. The equilibrium equations and natural boundary conditions are derived by the principle of virtual power. To validate the new proposed model, different cases in bending, buckling and free vibration have been considered.

A comparative study on different ways to determine the mechanical properties of four glass fiber composite materials, two of which with orthotropic behaviour, is developed in this paper. This work highlights the accuracy of the results obtained by means of a low cost dynamic characterization method which is developed as part of nondestructive evaluation by ultrasonic wave velocities measurement, compared to a static characterisation method by tensile testing.

This work presents a new composite beam model based on discrete layer theory. It enables the automatic verification of the continuity of transverse shear stresses by taking into account the Heaviside step function. The transverse shear is represented by a sine function which improves the accuracy of the results on the transverse shear stress. The membrane refinement cosine function improves the warping of the straight section in bending deformations. In order to validate the proposed model, several problems in bending and free vibration are presented. For sandwich composite beams, the proposed new model satisfies exactly and automatically the continuity conditions of displacements and stresses at the interfaces, as well as the boundary conditions.

The aim of the presented investigations is to perform an analysis of fracture and instability during simple and complex load testing by addressing the influence of ductile damage evolution in necking processes. In this context, an improved experimental methodology was developed and successfully used to evaluate localization of deformation during uniaxial and biaxial tensile tests. The biaxial tensile tests are carried out using cruciform specimen loaded using a biaxial testing machine. In this experimental investigation, Stereo-Image Correlation technique has is used to produce the heterogeneous deformations map within the specimen surface. Scanning electron microscope is used to evaluate the fracture mechanism and the micro-voids growth. A finite element model of uniaxial and biaxial tensile tests are developed, where a ductile damage model Gurson–Tvergaard–Needleman (GTN) is used to describe material deformation involving damage evolution. Comparison between the experimental and the simulation results show the accuracy of the finite element model to predict the instability phenomenon. The advanced measurement techniques contribute to understand better the ductile fracture mechanism.

International audience; The complex mechanical behaviour of composite materials, due to internal heterogeneity and multi-layered composition impose deeper studies. This paper presents an experimental investigation technique to perform volume kinematic measurements in composite materials. The association of X-ray micro-computed tomography acquisitions and Digital Volume Correlation (DVC) technique allows the measurement of displacements and deformations in the whole volume of composite specimen. To elaborate the latter, composite fibres and epoxy resin are associated with metallic particles to create contrast during X-ray acquisition. A specific in situ loading device is presented for three-point bending tests, which enables the visualization of transverse shear effects in composite structures.

International audience; The present work is devoted to damaging process in carbon-fiber reinforced laminated composites. An original experimental approach combining three optical measurement techniques is presented. Image stereo-correlation and infrared thermography, that respectively provide the kinematic and thermal fields on the surface of the composites, are used in live recording during axis and off-axis tensile tests. Special attention is paid to simultaneously conduct these two techniques while avoiding their respective influence. On the other hand, X-ray tomography allows a post-failure analysis of the degradation patterns within the laminates volume. All these techniques are non-destructive (without contact) and offer an interesting full-field investigation of the material response. Their combination allows a coupled analysis of different demonstrations of same degradation mechanisms. For instance, thermal events and densimetric fields show a random location of damage in the early stages of testing. The influence of the material initial anisotropy on damage growth, localization and failure mode can also be clearly put in evidence through various data. In addition to such characterization, this study illustrates at the same time the capabilities of the different full-field techniques and the damage features they can best capture respectively.

The present study analyses an aircraft composite fuselage structure manufactured by the Liquid Resin Infusion (LRI) process and subjected to a compressive load. LRI is based on the moulding of high performance composite parts by infusing liquid resin on dry fibres instead of prepreg fabrics or Resin Transfer Moulding (RTM). Actual industrial projects face composite integrated structure issues as a number of structures (stiffeners, …) are more and more integrated onto the skins of aircraft fuselage. A post-buckling test of a composite fuselage representative panel is set up, from numerical results available in previous works. Two stereo Digital Image Correlation (DIC) systems are positioned on each side of the panel, that are aimed at correlating numerical and experimental out-of-plane displacements (corresponding to the skin local buckling displacements of the panel). First, the experimental approach and the test facility are presented. A post-mortem failure analysis is then performed with the help of Non-Destructive Techniques (NDT). X-ray Computed Tomography (CT) measurements and ultrasonic testing (US) techniques are able to explain the failure mechanisms that occured during this post-buckling test. Numerical results are validated by the experimental results.

Thin-walled textile-reinforced composite parts possess excellent properties, including lightweight, high specific strength, internal torque and moment resistance which offer opportunities for applications in mass transit and ground transportation. In particular, the composite material is widely used in aerospace and aircraft structure. In order to estimate accurately the parameters of the constitutive law of woven fabric composite, it is recommended to canvass multi-scale modeling approaches: meso, micro and macro. In the present investigation, based on the experimental results established by carrying out observations by Scanning electron microscope (SEM), we developed a micro-scale FEM model of carbon-fiber reinforced thermoplastic using a commercial software ABAQUS. From the SEM cartography, one identified two types of representative volume elementary (RVE): periodic and random distribution of micro-fibers in the yarn. Referring to homogenization method and by applying the limits conditions to the RVE, we have extracted the coefficients of the rigidity matrix of the studied composites. In the last part of this work, we compare the results obtained by random and periodic RVE model of carbon/PPS and we compute the relative error assuming that random model gives the right value.

La technique de reparation/renforcement des structures de genie civil en beton par composites colles est aujourd’hui couramment utilisee en France. Elle constitue l’un des outils permettant d’augmenter la duree de vie des parcs d’ouvrages en beton. Dans le cas des ouvrages en acier, son utilisation reste cependant beaucoup plus limitee. Ceci resulte sans doute du fait que les materiaux composites et l’acier presentent des rigidites tres voisines, mais aussi de l’apprehension a utiliser le collage structural comme methode d’assemblage. Dans le cadre d’une operation de recherche de l’IFSTTAR (Institut Francais des Sciences et Technologies des Transports, de l’Amenagement et des Reseaux), le Departement Laboratoire d’Autun s’est interesse aux assemblages colles entre renforts composites et supports metalliques de type acier Cet article rappelle dans un premier temps les domaines d’utilisation de la technique de collage ainsi que ses avantages, puis s’interesse a la caracterisation du transfert des efforts par collage entre materiaux composites et metal. L’influence du vieillissement hygrothermique (40°C, 95% d’humidite relative) ou de pseudo cycles de fatigue sur les caracteristiques de l’assemblage colle est ensuite etudiee afin evaluer la durabilite de l’interface composite/acier. Bien qu’il reste des sujets a approfondir, le travail realise montre que le renforcement par collage de materiaux composites est une technique viable pour les structures en acier.

International audience; FUSCOMP (FUSelage COMPosite) is a Research & Development program which has received the label from the Aerospace Valley competitiveness cluster. It will lead to a test of a composite fuselage demonstrator manufactured by the Liquid Resin Infusion (LRI) process. LRI is based on the moulding of high performance composite parts by infusing liquid resin on dry fibers instead of prepreg fabrics. The study of this proof of concept is based on the TBM 850 airframe, a pressurized business turboprop aircraft currently produced by DAHER-SOCATA. Technical achievements will concern numerical methods and finite elements analysis to be used for the modelling of this aircraft composite fuselage structure. Actual industrial projects face composite integrated structure issues as a number of structures (stiffeners,...) are more and more integrated onto the skins of aircraft fuselage. Indeed the main benefit of LRI is to reduce assembly steps which lead to cycle time gain and thus cost reduction. In particular, infusing components and sub-components at the same time avoids riveting parts altogether. However it is necessary to validate the dimensioning of the studied composite structure.

The aim of this work is to identify parameters driving constitutive equations of materials with displacement field measurements carried out by image stereo-correlation during an unidirectional tensile test. We evaluate two identification techniques. The first one is the virtual fields method which consists in writing the principle of virtual work with particular virtual fields. It is generally used in the case of linear elasticity and it requires a perfect knowledge of the model in terms of boundary condition since the virtual fields used must be kinematically admissible. This method allows to determine parameters by a direct and fast calculation, without iterations. The second method is the finite element model updating method. It consists in finding constitutive parameters that achieve the best match between finite element analysis quantities and their experimental counterparts. This method is more adaptable than the virtual field method but it needs to spend more calculation time.

The first aim of this study is to analyze the impact behavior of pre-loaded composite. Indeed, a bi-axial load is applied to the composite specimen, in order to keep in touch with a real case of composite fuselage. Then, this pre-loaded specimen is impacted by a pendulum. The used energy and velocity are weak in order to be in the case of low-energy and low-velocity impact. The second aim of this study is to develop and design a pendulum device to be integrated to the bi-axial fatigue loading. Moreover, two Non Destructive Inspections (Sonoscan and InfraRed Thermography) is used in order to establish links between pre-load and induced impact damage.

The aim of this study is to gain knowledge concerning the process and its physics, as well as to become able to optimize the fabrication of large and complex composite parts in aeronautics appli- cations. Composite materials have many advantages and the use of this technology is increasing in the aeronautic industry. In the L.R.I. process, dry textile preforms are impregnated by a thermoset liquid resin. All the elements are enclosed in a vacuum bag of known pressure. Once preforms are totally impregnated, the resin system begins the curing reaction to obtain the composite part. This study contains two major sections. Firstly, numerical modeling was done with the Pam- Rtm nite element code to determine the evolution of the ow front during the infusion. Simulations were performed to analyse the infusion of sandwich composite parts with a perforate foam, which allows the inferior skin to be impregnated in the same operation. Secondly, experimental work was conducted to conrm the numerical results.

On Airbus aircraft, spherical plain bearings are used on many components; in particular to link engine to pylon or pylon to wing. Design of bearings is based on contact pressure distribution on spherical surfaces. To determine this distribution, a 3D analysis of the mechanical behaviour of aeronautical plain bearing is presented in this paper. A numerical model has been built and validated from a comparison with 3D experimental measurements of kinematic components. For that, digital volume correlation (DVC) coupled with optical scanning tomography (OST) is employed to study the mechanical response of a plain bearing model made in epoxy resin. Experimental results have been compared with the ones obtained from the simulated model. This comparison enables us to study the influence of various boundary conditions to build the FE model. Some factors have been highlighted like the fitting behaviour which can radically change contact pressure distribution. This work shows the contribution of a representative mechanical environment to study precisely mechanical response of aeronautical plain bearings.

The aim of this work is to estimate errors related to Stereo-correlation technique applied to measurements of displacements. In a first step, the influence of the cameras positions is tested using a standard object. In a second step, an evaluation of the stereo-correlation system is achieved. It is based on the generation of synthetic images representative of real speckle patterns deformed. With these images, various parameters are treated in order to determine their impact on the measurement error.

The purpose of this work is to study the Iosipescu shear test and more precisely its ability to characterize the shear modulus of a carbone/epoxy composite material. The parameters influencing this identification are the fibre orientation, the geometry of the notch and the boundary conditions. Initially these parameters were studied through the finite element analysis of the shear test. Then, the measurement of the shear strains was carried out by traditional methods of measurement (strain gauges) but also by optical methods. These optical methods: the digital image correlation and the electronic speckle pattern interferometry (ESPI); allow for various levels of loading, to reach a full-field measurement of the shear strain. This enabled us to study the strain distribution on the section between the two notches. The finite element model enabled us to study the parameters influencing the calculation of the shear modulus in comparison with strain gauges, image correlation and ESPI. This work makes it possible to conclude on optimal parameters for the Iosipescu test.

This paper deals with the development of an experimental method to make measurements by the digital image correlation technique during a dynamic test on a biaxial tensile system. The aim of this method is to be able to cover a complete cycle of a dynamic test, regardless of its form and to follow a position during a long time test. Results are presented for different measurement fields.

National audience; Même si les performances des matériaux composites donnent de nouvelles perspectives pour la conception aéronautique et spatiale, la variabilité de leur comportement, liée à la présence de micro-défauts initiaux ou provoqués en service constitue néanmoins un frein important à leur développement. En s'intéressant plus particulièrement à la réponse de ces matériaux sous sollicitations de fatigue ou face au vieillissement, leur comportement est modifié par de nombreuses sources d'incertitude, notamment sur la nature des mécanismes physiques de dégradation, qui sont amplifiés par une forte dispersion durant leur cycle de vie. Dans l'industrie aéronautique, le phénomène d'impact n'est encore que peu connu concernant les matériaux et les structures composites. Le but de ce travail est de développer un modèle capable de prédire l'évolution, en termes de propagation d'un défaut présent dans une structure, en vieillissement mécanique, thermique, temporel, .... Nous devons déterminer quels paramètres sont prédominants lors du phénomène d'impact et comment ils agissent sur la structure. Pour ce faire, nous nous appuierons sur des travaux existants [1-5]. Ceux-ci déterminent un nombre important de paramètres (séquence d'empilement, vitesse ou énergie d'impact, forme de l'impacteur, angle d'incidence de l'impact, propriétés mécaniques de la résine, ...) et leur effet. Nous nous intéresserons aussi à l'influence du procédé de fabrication dans le comportement à l'impact. En s'appuyant sur un plan d'expériences, nous choisirons les paramètres les plus prépondérants ou les interactions les plus significatives. Il en résultera un nombre réduit de paramètres à prendre en compte lors de l'impact.

Long duration super-pressure balloon design and manufacturing is a great challenge for the CNES in scientific ballooning. They are made of thin polymer films which are joined with thermo-adhesive bands. To date, during flight missions, a real problem appears: some balloons explode prematurely. This study deals with the mechanical behaviour of the assembly of the constitutive parts. Firstly, a nanoindentation test campaign makes it possible to identify the elastic properties of the materials directly in the assembly. Then, we simulate a nominal assembly in 2D and 3D approaches. Finally, we use the factorial design method and finite element models to study the influence of the various conception parameters on the mechanical behaviour of the assembly., La modélisation et la fabrication des ballons pressurisés stratosphériques longue durée à usage scientifique sont un défi pour le CNES. Les ballons sont constitués de plusieurs fuseaux de film polymère, assemblés entre eux par des rubans thermo-adhésifs. A ce jour, un problème majeur apparaît lors des missions de vol se traduisant pour certains ballons par une destruction prématurée. Ce travail porte sur l'étude du comportement mécanique des assemblages des films polymères qui constituent l'un des points faibles présumé des ballons. Dans un premier temps, une campagne d'essais de nanoindentation nous permet d'identifier les propriétés élastiques des matériaux, une fois les matériaux assemblés. Dans un second temps, nous modélisons un assemblage nominal en approche 2D puis 3D. Enfin, à l'aide de la méthode des plans d'expériences et de simulations éléments finis, nous étudions l'influence des paramètres de conception sur la tenue mécanique de l'assemblage.

Colloque avec actes et comité de lecture. Internationale.; International audience; Pour étudier le comportement des éléments rotulés de mât-réacteur d'avions, AIRBUS cherche à construire un outil de simulation numérique par la méthode des éléments finis, permettant d'analyser l'influence de leur géométrie sur leur performance. Cet article présente le travail de comparaison entrepris pour valider la simulation numérique du comportement statique à l'aide d'une technique expérimentale d'investigation dans le volume : la photoélasticimétrie tridimensionnelle. Cette technique permet d'analyser la répartition 3D des contraintes dans des structures modèles fabriquées en résine époxy. Ces premières observations nous ont permis de faire évoluer le modèle numérique afin de le rendre plus réaliste.

National audience; Pour étudier le comportement des éléments rotulés de mât-réacteur d'avions, AIRBUS cherche à construire un outil de simulation numérique par la méthode des éléments finis, permettant d'analyser l'influence de leur géométrie sur leur performance. Cet article présente le travail de comparaison entrepris pour valider la simulation numérique du comportement statique à l'aide d'une technique expérimentale d'investigation dans le volume : la photoélasticimétrie tridimensionnelle. Cette technique permet d'analyser la répartition 3D des contraintes dans des structures modèles fabriquées en résine époxy. Ces premières observations nous ont permis de faire évoluer le modèle numérique afin de le rendre plus réaliste.

This work presents a new composite beam model based on discrete layer theory. It allows to verify automatically the continuity of transverse shear stresses by taking into account the Heaviside step function. Besides, the transverse shear is represented by a sine function (Touratier, 1991). Moreover, this model introduces membrane refinement (Ossadzow and al., 1995).